1. Field of the Invention
The invention relates to hydraulic cylinder mechanisms used for raising and lowering implements carried by powered vehicles.
2. Description of the Related Art
U.S. Pat. No. 4,920,732 illustrates a mowing vehicle having a mower deck coupled to a vehicle via a hydraulic cylinder assembly. Conventional cylinders have rods rigidly fixed to pistons within the cylinder, and can be actuated to selectively transfer the weight of the deck to the vehicle to enhance the vehicle's traction and stability during operation. These cylinders can also be actuated by the operators to lift the deck over curbs or other obstructions during transport.
During operation, the mower deck shown in U.S. Pat. No. 4,920,732 will roll over ground contours. The deck will rise up as it encounters a bump, and will therefore press upwardly on the rod to cause the piston to shift upwardly within the cylinder. Fluid will be drawn into the rod end of the cylinder in response to the piston shifting upwardly. The piston tends to shift upward rapidly, since the ground and deck press the rod and piston upwardly against the large weight of the vehicle. Fluid therefore enters the rod end of the cylinder quickly and does not undesirably slow the shifting of the piston.
Once the deck passes over the crest of a bump the front of the deck must tilt downwardly to remain in contact with the ground for continued mowing operations. To accomplish this, the weight of the deck acts to shift the piston downwardly within the cylinder. Fluid must be forced out of the rod end of the cylinder by the piston as it shifts downwardly. The small size of the opening in the cylinder and the pressure in the hydraulic circuit tend to resist the displacement of fluid from the cylinder. Since the weight of the deck, which is small compared to the weight of the vehicle, is the only force acting to shift the piston downwardly and force the fluid out of the cylinder, the downward shifting of the piston and deck thereattached is relatively slow. Therefore, once the deck has passed over the crest of a bump, the slow downward shifting of the deck may cause an area of vegetation to be left uncut by the mower.
Therefore, it would be desirable to provide a fluid cylinder assembly that can be selectively actuated for weight transferral or lifting of the implement, and that allows the implement to follow the contours of the ground. It would be desirable to provide such a cylinder with a mechanism that allows t he deck to rapidly shift downwardly to remain in contact with the ground after ground undulations have been encountered such that little or no areas of grass are left uncut. It would also be desirable for such a mechanism to be internally provided by the workings of the cylinder.